What is CVE-2023-33009?

CVE-2023-33009 is a critical-severity vulnerability in Zyxel Atp100, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2023-05-24.

How severe is CVE-2023-33009?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2023-33009 known to be exploited?

Yes. CVE-2023-33009 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-05), indicating it is being actively exploited. 3 public proof-of-concept repositories are indexed.

Buffer overflow in Zyxel Atp100

CVE-2023-33009

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX series firmware versions 4.60 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.60 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.60 through 5.36 Patch 1, VPN series firmware versions 4.60 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.60 through 4.73 Patch 1, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and even a remote code execution on an affected device.

Vulnerability class: Buffer Overflow

Published 2023-05-24 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.281 (98.1th percentile), scored 2026-10-18.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 98th percentile — 98.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.281 · newest: 0.281 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2023-06-05. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2023-06-26.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for… (Vendor Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2023-33009?: CVE-2023-33009 is a critical-severity vulnerability in Zyxel Atp100, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.8/10. Published 2023-05-24.
How severe is CVE-2023-33009?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2023-33009 known to be exploited?: Yes. CVE-2023-33009 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-05), indicating it is being actively exploited. 3 public proof-of-concept repositories are indexed.